Manufacture of vesicular glass



Oct 28, 1941. H Fox HAL 2,261,922

MANUFACTURE OF VESICULAR GLASS Filed Dec. 24, 1957' 4 Sheets-Sheet lmwzzvmn. 'J oHM h Fox By WILL/[31.0 LYTLE,

Get. 28, 1941. J. H. Fox ETAL MANUFACTURE OF VESICULAR GLASS Filed Dec.24, 1937 4 Sheets-Sheet 2 mww Oct. 28,, 141. j FQX ET AL 2 261 922MANUFACTURE OF VESICULAR GLASS INVENTOR. Jail/v 4 Fax MAL/HM OLYT ARNEYS.

0% J. H. FOX arm.

MANUFACTURE OF VESICULAR GLASS Filed Dec. 24, 1937 4 Sheets-Sheet 4 wwuINVENIDR. Jbmv H Fox BY WILL/7M 0 B 9/514.

A RNEYS.

Patented Oct. 28, 1941 MANUFACTURE OF VESICULAR GLASS John H. Fox,Pittsburgh, and

William Lytle, New Kensington, Pa., aleignors to Pittsburgh Plate GlassCompany, a corporation of Pennsylvania Application December 24, 1937,Serial No. 181,830

3 Claims. (Cl. 48-83J) The present invention relates to the manufactureof glass products and it has particular relation to the manufacture of aporous glass product suitable for use as a means for heat and soundinsulation and as a light weight building material.

One object of the invention is to provide a process of manufacturingporous glass in which operation is substantially continuous and involvesa minimum expenditure of labor.

This and other objects will be apparent from consideration of thefollowing specification and claims.

It has heretofore been proposed to introduce bubbles of gas into moltenglass in order to form a cellular product which is an insulating mediumfor heat and sound. The conventional method of preparing the productinvolved the provision of a portion of molten glass containing bubblesof gas or containing a gas-producing material in molds and then allowingthe molten or plastic material to expand .to fill the mold. Obviously, asubstantial amount of labor is involved in such operation which tends toincrease the cost of the product.

According to the provisions of the present invention this objection isobviated by forming a foam or froth of molten or plastic glass in asuitable container by any convenient method, for example,- by blowingmolten glass with air or other gas or by whipping molten glass and thendrawing off the froth from the top of the mass as a continuous sheet andthen cooling the sheet and cutting it up into blocks or units ofsuitable size.

Embodiments of apparatus suitable for use in practicing the inventionare disclosed in the drawings in which Figure 1 is a cross-sectionalview of an apparatus for forming cellular glass and then drawing itvertically as a sheet. Figures 2 and 3 are cross-sectional views of anapparatus for forming molten cellular glass and then drawing ithorizontally into sheet form. Figure 4 is a cross-sectional view of aform of apparatus suitable for drawing the cellular product horizontallyand simultaneously forming it into blocks. In the drawings like numeralsrefer to like parts throughout.

In the form of the invention disclosed in Figure 1 a glass tank It has aroof or arch H and ports l2 for the admission of fuel Bases forcombustion to melt the glass. It is also provided at its forward endwith a downwardlyextending curtain or baille ii, that separates the mentII, and at its lower edge is spaced from the bottom of the tank It inorder to Provide a passage I. for the flow of molten glass from the tankll into the forehearth. Suitable means for converting the molten glasspassing from the tank I. into a froth or foamare provided and maycomprise a series of tuyere-like inlet tubes l1 extending upwardlythrough the bottom of the forehearth ll. These tubes communicate with atubular manifold it which is fed with air. carbon dioxide or othersuitable gas by means of a conduit IS. A gas-producing liquid such aswater may also be fed through the tube I, which liquid upon contact withthe molten glass in the bottom of the chamber is quickly converted byevaporization or chemical reaction into a gas which forms the bubbles.In order to insure that the bubbles in the glass will be broken up intosufllciently small sizes, a motor driven shaft 20 may extend upwardlythrough one of the inlet tubes I1 and is provided at its upper extremitywith an agitator blade 2 i. Gases passing up around the shaft preventescape of molten glass about the shaft and also tend to 7 means forheating the mass comprise a plurality of electrodes 22, adapted toconduct electricity directly into the molten glass, which are Joined toconductors 23 extending to a suitable source of electricity (not shown).If preferred these electrodes may be supplemented or even entirelyreplaced by horizontal fire tubes 24 which may be heated or cooled asrequired by means of combustion gasses or other gases from a suitablefurnace or compressor (not shown). Electrical resistance heatingelements may also be enclosed in these tubes if desired. A second set ofhorizontal tubes 26 are disposed above the electrodes 22 and constitutesmeans for further heating the molten glass or in event that it isdesired to increase the viscosity of the glass ad- Jacent to the surfacea cooling medium such as air or the like may be circulated therethrough.In case that heating alone is requirednthese tubes may be replaced orsupplemented by electrical resistances or electrodes.

An additional tube 21 placed adjacent to the upper surface of the moltenmass preferably is of trapezoidal cross-sectional contour and constitankfrom the forehearth or drawing comparttutes a draw-bar for purposes ofinitiating the forming of the glass sheet. Heat may be supplied to thisbar by means of heated gases passing therethrough or by means ofsuitable electrical resistances (not shown). For purposes of furtherincreasing the porosity of the molten glass passing over the bar, aseries of small holes or outlets 28 may be formed in the bar and all ora portion of the gases at suitable temperature introduced as bubblesinto the molten mass as it is formed into a sheet.

A series of pairs of spaced rollers 20, driven by suitable means (notshown), are arranged horizontally above the surface of the molten glassin the compartment l4 and constitute means for drawing and rolling themolten glass out into sheet form. If desired. the foamy mass as itemerges from the compartment Il may be quickly cooled upon its surfacein order to increase the viscosity and thus more securely to entrap thebubbles of gas contained therein during the early stages of drawing.Means for accomplishing this function comprises tubes II disposed uponthe opposite sides of the sheet as it is being formed and having formedtherein a series of nozzles 3| through which a cooling medium, such asair, is blown upon the sheet at the point of its formation. The mode ofoperation of this embodiment of the invention is relatively simple.Molten glass in tank II is allowed to flow through the passage ll intothe compartment it while a mass or bubble-forming gas is pro- Jectedthereinto through the inlets H. The temperature of the bubbly mass isthen adjusted at the various levels by means of the heating elements 22or tubes II and 28 in order to insure that it is of correct consistencyto maintain the entrapped bubbles of gas uniformly distributed in themass and also to insure that it can be drawn out into sheet form.Additional gases may be introduced through the conduit-like draw-bar 21.However, this may not in all instances be required. The mass above thedrawbar is then conducted between the rollers 29 which draw it out as acellular glass sheet, while a cooling gas from conduits 3| may beallowed to play upon the surface thereof.

If desired, the tank ll for feeding molten glass into the compartment Hmay be eliminated and the compartment simply charged with cullet or withsand, lime and soda in order to form the molten glass in situ in thecompartment. The gas for forming the bubbles instead of being introducedthrough the inlets I! may also be formed in the mass by chemicaldecomposition of a gas-forming material such as calcium carbonate or bythe combustion of carbonaceous materials under the surface of the glass.These gas-producing materials may be introduced directly into the moltenglass or may be admixed with crushed glass or with finely dividedglassforming materials which are then introduced as solid materials intothe compartment II where the glass or glass-forming materials are melteddown into a more or less fluid state and the gasforming materials aredecomposed to generate bubbles in the mass.

Apparatus for drawing sheets of cellular glass horizontally is disclosedin Figure 2 and comprises a tank 40 in which is dispoud a baffle orcurtain 4i dividing it into a melting tank 42 and a forehearth ordrawing chamber 43. Glass in molten state flows from the melting tankthrough a passage 44 below the lower edge of the baflle 4! into thedrawing compartment II, and may be converted into froth or foam by anysuitable means. For moses of illustration there is shown a feedermechanism for the introduction of calcium carbonate, vermiculite, orsimilar gasproducing or gas-containing substances through the bottom ofthe compartment into the stream of glass as it enters the drawingcompartment. This feeder mechanism comprises an inlet conduit 48extending through the bottom of the compartment 43 and being providedwith a screw conveyor 41, for forcing the solid gassing material intothe molten glass. The tube is connected at its lower end to the throatll of an air lock chamber ll, constituting means for preventing gasesgenerated by decomposition of the calcium carbonate at the bottom of thedrawing com means of a conduit It to assist in forming bubbles in themass and to prevent any tendency of the molten glass to percolatedownwardly through the granular material in tube 40. If preferred thelatter tendency may be obviated by elevation of the rear end of screw 41and tube II in such manner that the rear ends thereof are above thelevel of the glass. If desired the foam may be produced entirely bymeans of a gassing medium such as air, steam, or the like introduced influid form through the conduit N, or if preferred the foaming may beproduced solely by means of a solid material such as calcium carbonatewhich is introduced by the action of a screw 41.

Screw 41 projects at its lower end through a suitable packing (notshown) in the lower extremity of the tube 48 and is driven by anyconvenient means, for example by means of a worm gear I! engaging amotor actuated worm II.

The temperature of the glass in the drawing compartment ll may becontrolled by means of electrical heating devices, by tubes forconducting heating or cooling gases in heat exchange relation with themolten mass, or by any other suitable means. In the drawings are shown aseries of electrodes I9, placed at suitable points adjacent to thebottom of the compartment. The temperature of the mass adjacent to thesurface is controlled by means of tubes ll through which a heating orcooling medium may be circulated as required. Thme tubes may be providedwith outlets for the further gasiflcation of the molten mass.

Transverse feeding of the molten material at the surface of the mass forpurposes of drawing it out in sheet form is obtained by means of aconveyor or chain 62 composed of relatively refractory material andtrained about rollers '3 and N, the latter of which is rotated bysuitable means (not shown). The conveyor is provided at suitableintervals with blades ll extending outwardly therefrom and projectingalong the lower reach of the conveyor below the surface of moltenmaterial in the compartment 48. Conveyor 02 extends outwardly over theforward edge of the compartment ll in proximity to one extremity of asecond conveyor .1 which is trained about rollers 08, driven by suitablemeans (not shown). This conveyor constitutes means for yl sawaythevesieularmassofglassasitis forced out of the drawing compartment by theconveyor 62 and preferably extends through an annealing lehr (notshown). A third conveyor 69 is disposed above and in parallelism to theconveyor 61 at a suitable height to press or restrict the foamy massupon the conveyor 61 to'a desired thickness.

In the operation of this embodiment of the invention molten glass isallowed to flow into the drawing compartment 43 from tank 42 and whileit is passing through the throat or channel 44 calcium carbonate orother suitable gassing agent is extruded into the stream. The viscousbubbly mass rises in the drawing chamber or forehearth until it isenmeshed between the paddles 66 upon conveyor 62. The latter then forcesthe surface layer out upon conveyor 61 where it is allowed to solidifyand is then annealed and cut up into slabs of convenient dimensions.

In Figure 3 is shown an embodiment of apparatus for forming thevesicular sheet into blocks as it is drawn from the tank or chamber. Inthis embodiment of apparatus, a suitable melting chamber in the form ofa tank or compartment 10, corresponding substantially to the drawingcompartment 43 in Figure 2 is provided for receiving the batch whichincludes the bubble-forming material. Feeding mechanism H for supplyingthe batch to the chamber comprises an inlet conduit I12 whichcommunicates through an opening I13 into the bottom of the chamber 10and which is provided with a screw conveyor I15 for forcing theingredients of the mixed batch into the melting chamber. Suitabledriving gearing I16 rotates the screw conveyor from the lower endthereof and the lower end of the conduit is provided with a bearing heador end wall I11 which rotatably supports the lower end portion of thescrew conveyor.

A hopper I80 has a lower throat portion I82 communicating with the lowerend portion of the conduit I12 and has a central air lock chamber I83communicating at opposite extremities with the lower throat portion I82and an upper flaring mouth I85 in which the batch material is supplied.Suitable slide valves I86 and I81 disposed at the upper and lowerextremities, respectively, of the air lock chamber prevent back pressurefrom forcing any of the material rearwardly or upwardly through thethroat portion I82. These valves can be opened alternately in order thatthe glass-making ingredients can be received into the chamber I83, andto permit such ingredients to be fed through the throat portion I82 intothe conduit I12 from which they are forced into the melting chamber 10.

A conduit I88 communicating with the air lock chamber I83 and with asuitable source (not shown) of fluid or gas under pressure is providedto facilitate the passage of the batch through the conduit I12 into themelting chamber 10 and also to facilitate the forming of a foamy batchin the melting chamber.

The melting of the materials to proper consistency in the chamber 10 iseffected by means of electrical heating devices, such as electrodes I90mounted at suitable locations in an intermediate portion of the chamber.The portion of the batch adjacentlits upper surface is controlled bymeans of heating tubes I92 through which heating or cooling medium canbe circulated as required. These tubes can also be provided with outletsinside the melting chamber for further gasiflcation of the molten mass.This arrangement of apparatus is provided with a conveyor 12 trainedabout suitable driven rollers 13 and 14,

the former of which is disposed parallel to and Y in proximity to thesurface of the molten glass and the latter of which is spaced asubstantial distance above and in advance of the forward edge of thetank. A conveyor 15 corresponding to the conveyor 81 is disposed belowthe lowerreach of the upper conveyor and these two conveyors preferablyextend through a lehr 18 in which the glass is annealed and cooled downto a temperature suitable for handling. These conveyors are respectivelyprovided ,with cleats or lugs 11 and 18 which coact to cut or mold thesheet of glass into blocks of appropriate size as it is formed. It willbe noted that the roller at the forward end of the upper conveyor isspaced a sufficient distance above the lower conveyor to disengage theblades or lugs on the upper conveyor from the blocks before the latterreach the end of travel thereof. The rearward extremity of the upperconveyor is held in proximity to the lower conveyor by means of a roller19.

The operation of this form of the invention is identical with that ofthe form disclosed in Figure 2 except that the glass is melted orsoftened or formed in the drawing chamber and the sheet as it is drawnout and while still plastic is scored or cut into blocks.

A mixture of crushed glass and CaCOz may be introduced through thehopper mouth I85 and feeding conduit I12 into the melting chamber 10 vwhere the glass melts down and the calcium carbonate decomposes to formbubbles of CO2. If the lime sand and soda ash of the batch areintroduced in this way, the CO2 evolved will be entrapped in the moltenglass as it seeks to escape upwardly to form the cellular mass withoutintroduction of additional gassing agents. In the event that thecellular body is formed by heating a mixture of crushed glass andcalcium carbonate, a glass of the composition of ordinary sheet glassmay be employed. It should be so crushed or broken up that it will passthrough a 28 mesh screen, but it is retained by a mesh screen. Suchmaterial will sinter at about 1300 or 1400" F. and will flow as a pastyplastic mass at a temperature of about 1600 to 1750 F. At highertemperatures it melts down completely. Preferably it is formed orbloated into a cellular mass while in this intermediate. plastic state.Within this temperature range the particles of glass, although they weldtogether at the points of contact, they do not completely coalesce orflow together. The resultant sheet apparently contains voids resultingfrom incomplete fusing of the particles and also from liberation of thegas bubbles in the mass. The apparent density of this mass may be variedalmost at will, but for most purposes a product having a weight of 14-35pounds per cubic foot is satisfactory. The material may be easily cutand sawed and can be nailed without breaking.

Of course the cellular mass could be formed under such conditions thatthe particles will be completely fused together to form a bubbly mass,and such mode of operation is contemplated as being within the scope ofthe present invention.

In the form of the invention disclosed in Figure 4 a tank 85 is providedwith a drawing compartment 88 separated therefrom by a baflie 31 all ofwhich respectively correspond to tank 40, drawing compartment 43 andbaflle ll in the form of the invention disclosed in Figure 2. Moltenglass in the drawing compartment is converted into a froth or foam bymeans of a gas or a gas-forming liquid introduced through inlets IIwhich are supplied from a conduit II. A suitable agitator for thoroughlydistributing the bubbles of glass may be provided and includes shaft 90which is extended into the tank through a conduit 9| Joined to theconduit in such manner that the gas passing upwardly about the shaftfunctions both to cool it and to prevent molten glass from flowingdownwardly about it. The shaft is actuated by a motor 82 at the lowerextremity thereof. At its upper extremity it is provided with suitableagitator blades 03. The vesicular mass in the drawing compartment ismaintained at a suitable operating temperature by means of electrodes 81disposed adjacent to the bottom thereof and further by means of tubes 98for heating or cooling gases disposed at suitable elevations in thetank. Additional gassing medium for further increasing the porosity ofthe molten glass may be introduced through a conduit 99 having inletsllll extending through the forward wall of the drawing tank adiacent tothe point where the glass is drawn from the tank.

The upper edge of the forward wall of the compartment terminates in alip I! designed to discharge the surface portion of the foamy mass ofmolten glass outwardly under a smoothing or compressing rollers I03 upona suitable conveyor which may comprise a series of driven rollers orpreferably as shown in the drawing a conveyor chain I04 trained aboutsupporting and driving roller I05 and leading to a suitable annealinglehr (not shown).

For purposes of insuring the uniform feed of the molten glass from thedrawing compartment to the conveyor I a suitable pusher mechanism may beprovided. An example of such mechanism includes a horizontal rod illwhich is provided at its forward end with a blade lll adapted to dipbelow the surface of the molten mass. This rod projects rearwardlythrough a slot I" in the rear wall of the drawing compartment and issupported upon and actuated by a pair of parallel cranks I09 which aresecured upon and driven by shafts ill. The shafts in turn are journaledin bearings in a support 2. A blast of air for cooling the surface ofthe molten glass in the drawing compartment is supplied through aconduit H3 disposed above the rod I".

The mode of operation of this embodiment of the invention issubstantially the same as that of the form disclosed in Figure 2. Moltenglass flows from the tank 85 into the drawing compartment t6 and istransformed into a foam by gas or gas-forming liquid such as water whichis introduced through the inlets l8 and 9|. The temperature of the massis suitably regulated by means of the electrodes 91 and the tubes 8'.The surface of the mass is quickly cooled by means of a blast of airfrom the conduit H3, in order to render it sufficiently viscous toretain the bubbles. The rotation of the shafts III causes the rod ill totravel downwardly to dip the blade I" into the surface of the mass andthen to travel forwardly to push a portion of the material outwardlyover the lip III and upon the conveyor Ill. Subsequently continuedrotation of the shafts causes the pusher rod to rise to lift the bladeI" from the glass and then to retract to the initial drawing position.The foamy mass upon the conveyor III is carried forwardly through theannealing lehr for W of relieving the internal strains upon the glass.

In any of the embodiments of the invention disclosed in Figures 2, 3 and4, the devices for expediting the flow of glass from the drawing hearthmay be eliminated, and flow of glass out upon the conveyors II, II and Iobtained by gravity alone and/or by the pull of the conveyor upon thecellular mass. Conveyor rollers arranged at suitable intervals areconsidered as the equivalents of the continuous conveyors disclosed.

The present process may be employed in the formation of cellular glassweighing up to or pounds per cubic foot.

Although only the preferred forms of the invention have been shown anddescribed, it will be apparent to those skilled in the are that numerousmodifications may be made therein without departing from the spirit ofthe invention or the scope of the appended claims.

. What we claim is:

1. The process of forming cellular glass which comprises mixing crushedglass and calcium carbonate, continuously feeding the mixture into amelting chamber, heating the mixture in the chamber until the calciumcarbonate decomposes to form bubbles of carbon dioxide and to provide afoamy batch, and drawing of! the upper area of the foamy batch andcooling it in the form of a porous body.

2. A process of preparing cellular glass sheets which comprises forminga foam of fluid glass in a chamber, drawing of! the foam as a sheet atthe top of the chamber, and simultaneously introducing gas bubbles intothe foam at the line of draw, and subsequently annealing and cooling theresultant sheet while replenishing the foam from below.

3. A process of forming cellular glass, which comprises heating amixture of finely crushed glass and a gassing agent to a temperature ofabout 1600 to 1750 F. to weld the particles of glass together at theirpoints of contact without completely coalescing them, the gassing agentbeing decomposable at such temperature to liberate bubbles of glass inthe mass and thus to bloat

